An AC drive is an electronic device for providing stepless control of the torque and rotation speed of AC motors. The AC drive controls the rotation speed of a motor by changing the fixed voltage and frequency of the supply network to variable values.

1. ac
what is an
drive
and how does it
work?
An AC drive is an electronic device for providing stepless control of
the torque and rotation speed of AC motors. The AC drive controls the
rotation speed of a motor by changing the fixed voltage and frequency of
the supply network to variable values. Stepless speed control gives many
benefits, including energy savings, improved controllability for processes,
reduced mechanical stress, and a quieter work environment. AC drives
can be used as stand alone devices or as part of a larger configuration.
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2. ac drives
part of a system solution
AC drives have developed considerably since the first devices came on the
market towards the end of the 1960s. Advances made in microprocessor
and semi-conductor technology in particular have had a vital impact on
AC drives, although their main principles have not changed.
Automation systems and field buses have also developed rapidly. Large-
scale production processes have automation systems that control the
process via various field devices. Conventional field devices include
temperature and pressure sensors, and conventional actuators include
valves, screws and dosage nozzles.
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3. ac drives
part of a system solution
An AC drive can also be classified connection to the AC drive, and
as an actuator that is connected the protocol used can be Modbus
to the automation system via a TCP/IP, Ethernet/IP, ProfiNet or
field bus. Vacon’s AC drives can BACnet/IP. One reference worth
be fitted with many different mentioning is Terminal 5 at
field buses, such as Profibus DP, Heathrow Airport in London, where
Modbus RTU, LonWorks, BACnet all the air-conditioning fans are
MS/TP, CANopen and DeviceNet. A controlled by Vacon® AC drives
growing proportion of the AC drives with a Modbus TCP/IP interface.
supplied by Vacon are fitted with
a separate field bus card. Today
Ethernet is also used with a direct
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4. ac drives
part of a system solution
Drive systems for production lines for paper, steel etc. are called sectional
drives. In the past, these drives have been controlled by a separate drive
control PLC. Using fast field buses, sectional drives can nowadays be
controlled directly from the automation system, eliminating unnecessary
intermediate stages.
Sectional drives also have time-critical functions that require
communication between the AC drives. A good example of this is a Master-
Follower function, which is used when several sections of a process are
mechanically linked to each other. In this situation, the torque reference
and possibly the speed reference need to be transmitted from one drive
to another rapidly. Equipment manufacturers have developed their own
means for communicating between the AC drives for this purpose.
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5. ac drives
part of a system solution
Manufacturers today have such Vacon has several references for
high requirements for production sectional drives where AC drives
that no unplanned breaks in are connected directly to the
production are allowed. There automation system via a field bus.
are many factors in industrial Monitoring and parameterizing
production that can disrupt field tools are needed for calibrating
buses and communications. and for maintenance, and these
However, field buses are completely are connected to the AC drives via
reliable if they are installed a separate bus.
correctly. Most disruptions are in
fact due to faulty installation and
defective earth connections.
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6. ac drives
part of a system solution
This is part of a
presentation given
by Kurt Hoffman,
Product Marketing
Director,
Drives Systems,
Vacon, at a
seminar organized
by the Finnish
Society of
Automation
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